Evidence Based Nutrition

Introduction

Vitamin C has been found to be a crucial player in various aspects of the immune system (3), most plants and animals can synthesise vitamin C from glucose (sugar) however, humans and some other vertebrates lack the enzyme that allows this process therefore they have to get their vitamin C intake through their diet, (10). Vitamin C Is a water-soluble vitamin therefore storage capacity is low, the human body loses about 3% of its vitamin C content per day, due to this a regular adequate intake is required to prevent any deficiency (4, 3). Vitamin C can be found in most fruits and vegetables such as citrus fruits (oranges, lemons, limes) strawberries, green leafy vegetables, papaya, broccoli, bell peppers, food & drinks are now fortified with vitamin C or there is also supplementation.

Vitamin C is probably most known for its benefits on supporting the body’s immune system and helping reduce severity of symptoms from the common cold. This does this by enhancing immune responses and functions as an antihistamine, vitamin C may also help prevent and treat respiratory infections by enhancing various immune cell functions therefore this vitamin is necessary for the immune system to sustain an adequate response against pathogens whilst avoiding excessive damage to the host (3). Vitamin C also acts as an antioxidant in the body neutralising free radicals, reducing oxidative stress and repairing damaged cells (1). Vitamin C has been found to work with vitamin E, which is also an antioxidant, by restoring the antioxidant properties of vitamin E but also there may be benefits to regularly taking both these vitamins for the long term to prevent early Alzheimer’s disease (see Vitamin E blog), (2). Vitamin C is also important for the production of the protein collagen, vitamin C is required for collagen synthesis and increases collagen production in young and older aged humans (1). Collagen is a connective tissue that holds muscles, bones and other tissues together, it is also found in your skin and is important for good skin health. Potentially vitamin C has anti-inflammatory activity for the skin and could be used in conditions such as acne and rosacea (10). Other functions of vitamin C include:

• Aids in wound healing
• Aids in bone or tooth formation
• Strengthen blood vessel walls
• Increases absorption of iron
• Cofactor for a family of gene regulatory enzymes and hormones

Vitamin C plays apart in a lot of roles in the human body therefore it is super important on getting the adequate daily amount, currently the RDA for vitamin C in the UK is set at 40mg per day for 19 – 64-year-olds. Other RDA’s range from 45 – 90mg per day however, many experts believe this is too low and should be increased. 45 – 90mg is enough to prevent scurvy and protect against any deficiency but experts believe for optimal function daily intake should be more in the 100 – 200mg range (8). A diet that has 100-200mg of vitamin C a day provides adequate plasma concentration levels in healthy individuals and covers the general requirements for the reduction of chronic disease risks and optimise cell and tissue levels, taking 100-200mg per day is also a safe non-toxic amount therefore experts believe increasing RDA will provide optimal functioning of this vitamin (3, 8). 

Deficiency & Toxicity

Deficiency of vitamin C is more common than you would think and is still a major concern in some countries. There are several reasons to why this may occur in modern life and in countries that would be expected to have sufficient food supply, first of course is poor dietary habits/lifestyles. Smoking can affect vitamin C levels more specifically smoking tobacco, use of certain drugs such as oral contraceptives and environmental stress such as air pollution and noise pollution, various diseases and poor socioeconomic status (lack of access to nutritious food) can all play a part in effecting vitamin C status in the body (3, 1). These can increase a person’s risk of a deficiency; the most severe vitamin C deficiency is Scurvy. Signs of scurvy include poor wound healing, impaired immunity, bleeding of the gums, bruising, swollen painful legs and weakness (8). Scurvy is well known to of been discovered through sailors and pirates in the 16^th century spending a long time at sea developing symptoms and causing more than half of a ships fleets deaths. By 1796 British ships were instructed to include lemon juice in their crew cargo to prevent scurvy and by the late 1800’s it was widely accepted that scurvy was a nutritional disease, and the cure was fresh fruit and vegetables (8).

Toxic effects are rare of vitamin C due to it being a water soluble that the body excretes when in excess and being unable to be stored in the body for someone to experience toxic effects of this vitamin they would have to have a very high intake of over 2000mg per day over a long period as the upper limit intake for adults has been found to be 2000mg. Vitamin C overdoses can cause kidney stones, gout, diarrhoea and rebound scurvy (1). This is very hard through diet alone toxicity is more likely to be caused through supplementation. 

Decreases absorption & Increase absorption

As previously mentioned, things such as smoking, and pollution levels can affect a person’s vitamin C status therefore smokers may require up to 35mg more than the average healthy individual just to prevent from developing a deficiency (4). Tobacco use is common in India whether that is smoking or chewing a study found high prevalence of vitamin C deficiency in older people in India with 74% of those in the north and 46% of those in the south of India were found to be deficient and a further 15% and 28% had sub-optimal levels (7). It was also found that vitamin C levels were lower in users of tobacco (7). 

Vitamin C content of food can be decreased through prolonged exposure to heat cooking can decrease the vitamin C content of vegetables by 40% to 60%, therefore minimalizing the time cooking will benefit the content of vitamin C in that food (8). Steaming the veg may be the best way to cook the veg tom minimalise vitamin C content loss. Vitamin C content is also lost through storage as soon as the fruit or vegetable is picked the content of vitamin C starts to decrease, buying frozen fruit & veg are going to contain more vitamin C than the “fresh” products however, vitamin C content will still have decreased. Exposure to sunlight also can decrease vitamin C content of fruit and vegetables. 

Vitamin C absorption depends on the amount ingested at low dosage at a time absorption can be 70-90% whereas in high dosage this can decrease to below 50% absorbed (8). Therefore, moderate intake of vitamin C will improve its absorption. 

Athletes 

Ascorbic acid is involved in a variety of metabolic reactions related to exercise such as synthesis of hormones involved in stress reactions, synthesis and activation of neuropeptides, collagen and carnitine (6). This is why exercise then causes a raise in blood ascorbic acid levels as this is distributed throughout the body at different levels then a decline happens after prolonged exercise (6). Vitamin C can be lost through sweat and depending on the person, the exercise and the weather conditions (hot and humid) on top of the metabolic reactions this can decline a lot therefore it is important to then replenish lost vitamin C after vigorous prolonged exercise (5). Vitamin C has important roles to play during exercise, however, can it increase an athlete’s performance if regular levels or even higher levels of the vitamin is maintained. Well deficiency of vitamin C has been found to reduce physical performance substantially even at the marginal deficiency level (5). Although it may hinder athletic performance having a deficiency in the vitamin no studies have found any clear evidence saying that it can improve performance. There are still benefits to advising supplementing or increasing someone intake of vitamin C, it may be important for athletes to supplement with vitamin C as they often put their bodies through stress daily so their requirements may also be higher than a regular person (6). Vitamin C works with vitamin E, both are antioxidants, and it has been found supplementing with both can reduce muscle damage induced by exercise in female athletes (see vitamin E blog), (9). Vitamin C also has the ability to enhance iron absorption from plant-based sources therefore good for preventing iron deficiency anaemia which is prevalent amongst athletes especially female athletes (5). 

Conclusion

Vitamin C is a water-soluble vitamin that can be found in most fruit and vegetables. Vitamin C is most known for supporting the immune system and helping in reducing symptoms of the common cold. But vitamin C also acts as an antioxidant reducing oxidative stress and repairing damaged cells and is involved in many other metabolic reactions in the body such as being needed for the production of collagen a protein important for skin health. The UK RDA is currently set at 40mg with other RDA’s ranging from 45 – 90mg however experts believe this should be increased to as high as 200mg to cover general requirements and provides optimal function of the vitamin. Deficiency is more common than you would think in modern life but still not as common as it was in the 16^th century. A deficiency can cause scurvy which can lead to picking up infections which can cause serious harm and even death. Toxicity is very rare due to being a water-soluble vitamin C cannot be stored and is usually excreted once levels are too high however with supplementation this can be possible causing kidney stones, gout, diarrhoea to name a few symptoms. Athletes can benefit from an optimal intake of vitamin C also; however, this does not enhance performance in anyway but exercise causes stress on the body and as an antioxidant vitamin C can help with reducing that stress therefore helping in recovery. Being deficient in vitamin C would hinder an athlete’s performance therefore is safe to recommend a regular intake. Vitamin C along with vitamin E can help reduce muscle damage and also vitamin C helps with the absorption of iron therefore reducing anaemia risk which is prevalent amongst athletes. Vitamin C plays an important role in our bodies therefore a minimal of 40mg intake is advised with up to 200mg required for optimal function this may increase for athletes.

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• Everything You Need to Know About Vitamin C
• Vitamin D and the Winter Months
• Everything You Need to Know About Vitamin K
• The Mediterranean Diet
• Everything You Need To Know About Vitamin E

References

1. Bellows, L. and Moore, R. (2012) ‘Food and Nutrition Series.’ November. 
2. Boothby, L. A. and Doering, P. L. (2005) ‘Vitamin C and vitamin E for alzheimer’s disease.’ Annals of Pharmacotherapy, 39(12) pp. 2073–2080. 
3. Carr, A. and Maggini, S. (2017) ‘Vitamin C and immune function.’ Nutrients, 9(11) p. 1211. 
4. Delanghe, J. R., Langlois, M. R., De Buyzere, M. L., Na, N., Ouyang, J., Speeckaert, M. M. and Torck, M. A. (2011) ‘Vitamin C deficiency: More than just a nutritional disorder.’ Genes & Nutrition, 6(4) pp. 341–346. 
5. Gerster, H. (1989) ‘The role of Vitamin C in athletic performance.’ Journal of the American College of Nutrition, 8(6) pp. 636–643. 
6. Peake, J. M. (2003) ‘Vitamin C: Effects of exercise and requirements with training.’ International Journal of Sport Nutrition and Exercise Metabolism, 13(2) pp. 125–151. 
7. Ravindran, R. D., Vashist, P., K. Gupta, S., S. Young, I., Maraini, G., Camparini, M., Jayanthi, R., John, N., Fitzpatrick, K. E., Chakravarthy, U., Ravilla, T. D. and Fletcher, A. E. (2011) ‘Prevalence and risk factors for vitamin C deficiency in north and South India: A two centre population based study in people aged 60 years and over.’ PLoS ONE, 6(12). 
8. Schlueter, A. K. and Johnston, C. S. (2011) ‘Vitamin C: Overview and update.’ Journal of Evidence-Based Complementary & Alternative Medicine, 16(1) pp. 49–57. 
9. Taghiyar, M., Darvishi, L., Askari, G., Feizi, A., Hariri, M., Mashhadi, N. S. and Ghiasvand, R. (2013) ‘The Effect of Vitamin C and E Supplementation on Muscle Damage and Oxidative Stress in Female Athletes: A Clinical Trial.’ The National Library of Medicine, 4(1). 
10. Telang, P. (2013) ‘Vitamin C in dermatology.’ Indian Dermatology Online Journal, 4(2) p. 143.